Photoelectron Imaging of Doubly Charged Anions, -O2C(CH2)nCO2- (n=2-8): Observation of Near 0 eV Electrons Due to Secondary Dissociative Autodetachment

Journal Article · Wed Mar 17 00:00:00 EDT 2010 · Journal of Physical Chemistry A, 114(13):4524-4530

DOI:https://doi.org/10.1021/jp1011523· OSTI ID:982007

Xing, Xiaopeng; Wang, Xue B; Wang, Lai S

The hallmark of multiply charged anions is the repulsive Coulomb barrier (RCB), which prevents low energy electrons from being emitted in photodetachment experiments. However, using photoelectron imaging, we have observed persistent near zero-eV electrons during photodetachment of doubly charged dicarboxylate anions, -O2C(CH2)nCO2- (Dn2-, n = 2-8). Here we show that these low energy electron signals are well structured and are independent of the detachment photon fluxes or energies. The relative intensities of these signals are dependent on n, with maxima at n = 2, 4, 6. These near zero-eV electrons cannot come from direct photodetachment of the dianions and are proposed to come from decarboxylation of the product radical anions upon photodetachment of the parent dianions [•O2C(CH2)nCO2- → CO2 + •(CH2)nCO2-], followed by dissociative autodetachment [•(CH2)nCO2- → (CH2)n + CO2 + e] or hydrogen-transfer-induced electron detachment [•(CH2)nCO2- → CH2=CH(CH2)n-2CO2H + e]. Energetic considerations suggest that these processes are exothermic. It is further observed that solvation by one water molecule quenches the low energy electron signals in the spectra of Dn2-(H2O), consistent with the proposed mechanisms. These indirect dissociative autodetachment processes are expected to involve cyclic transition states for n > 2, in agreement with the dependence on the chain length due to the anticipated strains in the intermediate steps. The quenching of the low energy electron signals by one water molecule demonstrates the importance of solvation on chemical reactions. ________________________

• Research Organization: Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 982007
• Report Number(s): PNNL-SA-69019; 25395; KC0301020; TRN: US1003989
• Journal Information: Journal of Physical Chemistry A, 114(13):4524-4530, Vol. 114, Issue 13
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
AGREEMENTS
ANIONS
CHAINS
CHEMICAL REACTIONS
COULOMB FIELD
DECARBOXYLATION
ELECTRON DETACHMENT
ELECTRONS
ENERGY
LENGTH
MOLECULES
PHOTONS
QUENCHING
RADICALS
SIGNALS
SOLVATION
SPECTRA
STRAINS
WATER
WELLS
Environmental Molecular Sciences Laboratory